1. Field of the Invention
The present invention generally relates to a printing system and printing method using a lithographic press. More specifically, the present invention relates to a paricular type of printing system, such as a newspaper printing system, which includes a plurality of printing rollers arranged in parallel to the axis of a plate cylinder.
2. Description of the Related Art
It is well known that a lithographic printing method utilizes the typical repulsion phenomenon that occurs between water and oil ink, or between silicone and oil ink, to form various printing images. In such a method, image areas are non-image areas and formed on a substantially similar plano-surface of a printing plate, and then oil ink is supplied to the image sections to print the image on any required material, such as paper.
For example, many newspaper printing factories employ a double sized rotary press capable of printing on four pages at once. See for example, "Newspaper Manufacturing Technical Words", pp. 358, (conventional Art 1), published by Nippon Newspaper Association on Jun. 11, 1990. One typical structure of this type of printing apparatus is shown in FIG. 5 and includes a plurality of printing plates P, each of which has a thickness of about 0.3 mm and a width accommodating single or double pages. The printing plates P are securely arranged in parallel to the axis of a plate cylinder PC regardless of the existence of images. Ink is supplied to all the printing plates P at the same time from an ink dispenser 1. In the drawing, D, BC, IC and W represent a dampening means, a blanket cylinder, an impression cylinder, and a paper web, respectively.
Methods for washing/cleaning printing cylinders are well known as reflected in Japanese Patent Application Laid Open Publications No. 63-288754/1988 entitled "Cleaning Device for Cylinders in Printing Apparatus" (Conventional Art 2) and No. 2-141241/1990 entitled "Cleaning Device for Plate Cylinder and/or Blanket Cylinder" (Conventional Art 3).
The device disclosed in the conventional art 2 is designed so that the circumferential surface of the cylinder is cleaned by a cloth when the surface is soiled during a continuous printing operation, and is provided with a system which automatically detects any gaps such as grooves, openings, and the like in the cylinder. This gap detecting system prevent any gaps from being soiled by the cleaning cloth which is itself soiled during the cleaning operation.
The conventional art 3 discloses a cleaning device for removing any dirt, dust, or remaining ink from the circumferential surface of the plate cylinder and/or blanket cylinder. This cleaning device can perform the cleaning operation over several portions and/or broad areas, at the same time.
In the above mentioned newspaper press, especially in a color printing operation, a page with a non-image sometimes appears adjacent to a page printed with images. Since an ink dispenser feeds ink to all the plate cylinders, every cylinder is provided with a printing plate regardless of the presence of images, to prevent the surface of the plate cylinders from adhering with the supplied ink. If the plate cylinder corresponding to the page with non-image is not covered with a printing plate, the supplied ink will easily be transferred to the paper web from the cylinder surface. In this system the printing plate without images is used only for protecting the paper web from being soiled with ink during the printing operation, and therefore prevents the wasting of ink. This system increases manufacturing costs because it requires plate producing work, in addition to the plate itself.
The lithographic printing system, which uses the repelling function between oil ink and water, requires a dampening means for feeding water to the non-image area of each printing plate, thereby ensuring that the non-image area is free from ink. This dampening water may flow back to an inking dispenser, thus decreasing ink concentration, which may cause stripping; i.e., an inking roller of the inking system may repel ink, thereby interfering with the printing operation. A non-image printing plate, needs more dampening water, in comparison with normal printing plates that include images, and non-images. Accordingly, a lithographic such non-image printing plate may produce poorly printed sheets for a long time.
The above described devices shown in the conventional arts 2 and 3, also require the use of printing plates corresponding to blank pages. It is apparent that these two conventional devices can not resolve the problems described above.